Electrolysers of filter press type are commonly used for the production of hydrogen and oxygen from brines and lyes, usually aqueous alkali hydroxide solutions. Cell stacks in such configurations are formed by electrochemical cells which commonly consist in sequence of a bipolar plate, first electrode (anode or cathode), a steel frame with a diaphragm, referred to as the diaphragm element, said diaphragm element separates the cell into anode and cathode compartment, a second electrode and a new bipolar plate. Gaskets are used for sealing purposes.
The manufacturing of inter alia diaphragm elements comprises both mechanical and/or manual fastening of the diaphragm to a frame and requires in addition gaskets to form a sealed cell stack. Another prior art embodiment comprises a moulding process to cover a steel frame with rubber and in such an assembly the bipolar plate is the load carrying element. The steel frame in the diaphragm element is only a means of fastening diaphragms while the rubber on the frame serves as gasket between neighbouring bipolar plates. Further, this existing assembly requires bipolar plates which have an outer diameter at least equal to that of the diaphragm frame thus covering the whole frame. As the bipolar plates are made of steel, this leads under normal operation to secondary electrolysis in the gas channels thereby reducing the gas quality. The existing assembly requires manual stacking where each element is placed in a vertical position. In the mentioned prior art embodiment the diaphragm elements with the integrated gasket form the seal between two bipolar plates. The mentioned embodiments are not suitable for pressurised operation. An increased internal pressure has to be compensated solely by the force exerted by bolts connecting the endplates arranged at each end of the stack. Hence an increased internal pressure may easily lead to leakages. The bipolar plates are supporting the electrolyser, but also bring the electrical potential to the outside of the electrolyser and complicate the electrical insulation of the device.
EP0833963B1 describes steel frames covered by vulcanizable material, i.e., rubber. This rubber serves as electrical insulation and as sealing material. The diaphragm is bolted to the rubber covered frame. Furthermore, a T-shaped element that forms the lye channels is bolted to the frame.
U.S. Pat. No. 6,554,978 discloses a high pressure electrolyser and frames thereof. The frames can be made of metal with a non-conducting layer or of a synthetic material. A separate gasket is included between the frames in the disclosed embodiments.
GB1145751 describes an electrolyser built up of frames that are formed of a hardenable mouldable material; examples of this material are cement, ceramic, thermosetting resin, thermoplastic materials. A separator may be integrally moulded to the frame ring. Rubber O-rings are included to provide the sealing between the frame and adjacent elements.
Traditionally electrodes are mounted by solid spacer, serving as a current collector, to the bipolar plate and there is a gap between electrode and diaphragm where gas bubbles are formed and escape into the gas collecting chambers.
According to prior art mounting of electrodes on bipolar plate is time-consuming and expensive. The gas-tightness of bipolar plate is compromised by drilling-through, which may lead to gas leakages especially during the pressurized operation. In addition current is concentrated in fewer spots which lead to non-uniform current distribution across the electrodes. Further, rigid fixing of electrode prevents intimate and adjustable contact of electrode with membrane as in a zero gap design, thus increasing the ohmic resistance and decreasing the efficiency of the electrolysis.
Processes concerning modules for electrolysers of filterpress type and for manufacturing of diaphragm elements according to prior art are laborious and demanding as many separate elements has to be fitted together.